In this tutorial, we will learn to create an abstract background in Illustrator CS3.
Make a rectangular path and fill blue gradient.
For the Gradient window choose blue and light blue colours.
Apply the gradient.
Then draw paths in new layers and paint them.
Then, move to Blend Options and choose the following settings:
Go to Object > Blend > Make.
This is the result you get after this step.
To get this great design.